If you read markdown into a QTextEdit, you can have checkboxes. Say you have a todo list, with todo and done categories being separate lists, and you want to cut a task from the todo list and paste it into the done list. The checkbox goes missing, and it becomes a plain list item with a bullet. Not sure if this bug is in the widget,
or more likely, missing support to "remember" QTextBlockFormat::marker() within the fragment that is on the clipboard.